Portable Oxygen Concentrator

ABSTRACT

A portable oxygen concentrator includes a pair of sieve beds, a compressor for delivering air to the sieve beds, a reservoir receiving oxygen-enriched gas from the sieve beds, and an air manifold attached to the first ends of the sieve beds. A set of valves operate under the control of a controller for selectively opening and closing the valves to alternately charge and purge the sieve beds to deliver oxygen-enriched gas into the reservoir. In addition, an exhaust passage communicates with the plurality of sieve beds to deliver a flow of nitrogen evacuated from the sieve beds such that the flow of the nitrogen is directed at or across the controller to cool the controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 11/099,783, filed Apr. 5, 2005, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to apparatus and methods forproviding oxygen, and, more particularly, to portable apparatus forconcentrating oxygen by adsorption from air and methods for using suchapparatus.

2. Description of the Related Art

Lung diseased patients often need supplemental oxygen to improve theircomfort and/or quality of life. Stationary sources of oxygen areavailable, e.g., oxygen lines in hospitals or other facilities, that mayprovide oxygen to patients. To allow some mobility, cylinders of pureand/or concentrated oxygen can be provided that a patient may carry orotherwise take with them, e.g., on pull-along carts. Such cylinders,however, have limited volume and are large and heavy, limiting thepatient's mobility.

Portable devices have been suggested that concentrate oxygen fromambient air to provide supplemental oxygen. For example, pressure swingadsorption (“PSA”) apparatus are known that separate nitrogen fromambient air, delivering a stream of concentrated oxygen that may bestored in a tank or delivered directly to patients. For example, U.S.Pat. Nos. 5,531,807 6,520,176, and 6,764,534 disclose portable PSAoxygen concentrators.

Accordingly, apparatus and methods for providing oxygen would be useful.

SUMMARY OF THE INVENTION

The present invention is directed generally to apparatus and methods forproviding oxygen. More particularly, the present invention is directedto portable pressure swing adsorption (“PSA”) apparatus forconcentrating oxygen and methods for using such apparatus.

In accordance with one embodiment, a portable oxygen concentrator isprovided that includes a plurality of sieve beds adapted to absorbnitrogen from air, each sieve bed comprising an air inlet/outlet end andan oxygen inlet/outlet end. At least one reservoir communicates with theoxygen inlet/outlet ends of the plurality of sieve beds for storingoxygen exiting from the oxygen inlet/outlet ends of the plurality ofsieve beds. A compressor delivers air at one or more desired pressuresto the air inlet/outlet ends of the plurality of sieve beds. A set ofvalves between the compressor and the air inlet/outlet ends of theplurality of sieve beds operates under the control of a controller,which selectively opens and closes the valves to alternately charge theplurality of sieve beds by delivering compressed air into the pluralityof sieve beds through the air inlet/outlet ends to cause oxygen-enrichedgas to exit from the oxygen inlet/outlet ends into the reservoir andpurge plurality of the sieve beds by evacuating pressurized nitrogenfrom the plurality of sieve beds through the air inlet/outlet ends.Also, an exhaust passage communicated with the air inlet/outlet ends ofthe plurality of sieve beds. The exhaust passage is configured todeliver a flow of nitrogen evacuated from the plurality of sieve bedssuch that the flow of the nitrogen is directed at or across thecontroller to cool the controller.

In another embodiment, a method is provided for concentrating oxygenusing a portable apparatus comprising a plurality of sieve beds, eachsieve bed including a first end and a second end, a reservoircommunicating with the second ends of the plurality of sieve beds, acompressor, a set of valves between the compressor and the first ends ofthe plurality of sieve beds, and control electronics adapted to controloperation of the valves. The method includes selectively opening andclosing the valves to alternately charge the plurality of sieve beds bydelivering compressed air into the plurality of sieve beds through thefirst ends to cause oxygen-enriched gas to exit from the second endsinto the reservoir and purge the plurality of sieve beds to evacuatepressurized nitrogen from the plurality of sieve beds through the firstends. In addition, the method further includes directing the nitrogenevacuated from the sieve beds at or across the control electronics tocool the control electronics.

These and other objects, features, and characteristics of the presentinvention, as well as the methods of operation and functions of therelated elements of structure and the combination of parts and economiesof manufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only andare not intended as a definition of the limits of the invention. As usedin the specification and in the claims, the singular form of “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are perspective top and bottom views, respectively, of afirst embodiment of a portable oxygen concentrator apparatus[ ];

FIG. 2 is an exploded perspective view of the apparatus of FIGS. 1A and1B[ ];

FIG. 3 is a schematic of the apparatus of FIGS. 1A and 1B[ ];

FIG. 4 is a cross-section of an exemplary sieve bed that may be includedin the apparatus of FIGS. 1A and 1B[ ];

FIG. 5 is a top cross-sectional view of a compressor that may beincluded in the apparatus of FIGS. 1A and 1B[ ];

FIG. 6 is a top view of a manifold base that may be part of an airmanifold of the apparatus of FIGS. 1A and 1B[ ];

FIGS. 7A and 7B are bottom and top views, respectively, of a manifoldcap that may be attached to the manifold base of FIG. 6[ ];

FIGS. 8A and 8B are perspective views of upper and lower sides amanifold base that may be part of an oxygen delivery manifold of theapparatus of FIGS. 1A and 1B[ ];

FIGS. 9A-9C are bottom, side, and top views, respectively, of a sievebed cap that may be part of the apparatus of FIGS. 1A and 1B[ ];

FIG. 10 is a graph showing pressure drop of air flowing through apassage as a size of the passage increases based upon exemplary averageflow rates[ ]; and

FIG. 11 is a graph showing the ratio of delivered concentrated oxygen toequivalent pure oxygen.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Turning to the drawings, FIGS. 1A-3 show a first embodiment of aportable oxygen concentrator apparatus 10. Generally, the apparatus 10includes a plurality of sieve beds or tanks 12, a compressor 14, a loweror air manifold 16 defining a plurality of passages 62-68 therein, astorage tank or reservoir 18, a set of air control valves 20 forcreating one or more flow paths through the passages 62-68 within theair manifold 16, and an upper or oxygen delivery manifold 102. Acontroller 22 may be coupled to the air control valves 20 forselectively opening and closing the air control valves 20 to controlairflow through the air manifold 16, and, consequently, through thesieve beds 12. Optionally, the apparatus 10 may include one or moreadditional components, e.g., one or more check valves, filters, sensors,electrical power sources (not shown), and/or other components, at leastsome of which may be coupled to the controller 22 (and/or one or moreadditional controllers, also not shown), as described further below. Itwill be appreciated that the terms “airflow,” “air,” or “gas” may beused generically herein, even though the particular fluid involved maybe ambient air, pressurized nitrogen, concentrated oxygen, and the like.

Turning to FIG. 4, each sieve bed 12 includes an outer casing 30, e.g.,in the shape of an elongate hollow cylinder, including a first or airinlet/outlet end 32 and a second or oxygen inlet/outlet end 34. Thecasing 30 may be formed from substantially rigid material, e.g.,plastic, such as acrylonitrile butadiene styrene (“ABS”), polycarbonate,and the like, metal, such as aluminum, or composite materials. Inexemplary embodiments, the casing 30 may have a diameter between abouttwo and ten centimeters (2-10 cm), and a length between about eight andthirty centimeters (8-30 cm). Although the casing 30 is shown having around cylindrical shape, it will be appreciated that the casing 30 mayhave other desired shapes, e.g., that may depend upon spatial,performance, and/or structural criteria. For example, the casing 30 mayhave an elliptical, square, rectangular, or other regular or irregularpolygonal shaped cross-section (not shown).

The casing 30 may be at least partially filled with filtration media orsieve material 36 to provide a sieve bed 12 capable of adsorbingnitrogen from air delivered into the sieve bed 12 under pressure. Tohold the sieve material 36 within the casing 30, the sieve bed 12 mayinclude discs or plates 38 adjacent each of the first and second ends32, 34 of the casing 30. The plates 38 may be spaced apart from oneanother to define a desired volume between the plates 38 and within thecasing 30. For example, the desired volume may be between about onehundred fifty and six hundred cubic centimeters (150-600 cm³), which maybe filled with sieve material 36. In an exemplary embodiment, the volumeof sieve material 36 within the sieve bed 12 may be about forty fourcubic inches (44 in³), as explained further below.

The plates 38 may include one or more openings or pores (not shown)therethrough to allow airflow through the plates 38. For example, theplates 38 may be formed from sintered plastic, thereby providing poreswithin the plastic material smaller than the grain size of the sievematerial 36 that allow airflow through the plates 38. Alternatively, theplates 38 may be formed from plastic, metal, or composite materialshaving multiple holes or pores formed therethrough. For example, theholes may be created when the plates 38 are formed, e.g., by molding theplates 38 and holes simultaneously. In another alternative, the plates38 may be formed as solid panels, e.g., cut from stock, molded, etc.,and the holes may be created through the panels, e.g., by drilling,laser cutting, and the like.

Generally, the sieve bed 12 may be filled such that there are nosubstantial voids in the sieve material 36, e.g., such that the sievematerial 36 is substantially packed between the plates 38. The resultingsieve bed 12 may weigh between about 0.25-1.50 pounds.

In the embodiment shown, the lower plate 38 a is substantiallystationary, e.g., fixed to the first end 32 of the casing 30, e.g., byone or more cooperating connectors or fasteners (not shown), adhesives,sonic welding, and the like. The upper plate 38 b may be disposedadjacent the second end 34, yet movable within the casing 30. Forexample, the upper plate 38 b may be biased towards the lower plate 38a, e.g., by a spring or other biasing mechanism 39, which may compressthe sieve material 36 between the plates 38. If the sieve material 36settles or somehow escapes from the sieve bed 12, the upper plate 38 bmay automatically move downwardly towards the lower plate 38 a tomaintain the sieve material 36 under a desired compression. Thiscompression may prevent the sieve material 36 from moving into otherareas of the apparatus 10 when it has become powderized from operationand/or may counteract flow-induced forces that may otherwise cause thesieve material 36 to fluidize.

The porosity of the plates 38 may be substantially uniform across thecross-section of the sieve bed 12, e.g., to ensure that flow into and/orout of the sieve bed 12 is substantially evenly distributed across thearea of the first and second ends 32, 34. Alternatively, the porosity ofthe plates 38 may be varied in a desired pattern, or only a portion ofthe plates 38 may be porous. In yet another alternative, the plates 38may have a solid wall and may include one or more openings therethrough,e.g., in a desired pattern.

The sieve material 36 may include one or more known materials capable ofadsorbing nitrogen from pressurized ambient air, thereby allowing oxygento be bled off or otherwise evacuated from the sieve bed 12. Exemplarysieve materials that may be used include synthetic zeolite, LiX, and thelike, such as UOP Oxysiv 5, 5A, Oxysiv MDX, or Zeochem Z10-06. It may bedesirable to provide multiple layers of sieve material 36 within thesieve bed 12, e.g., providing sieve material with different propertiesin layers between the first end 32 and the second end 34.

For example, because sieve material generally absorbs water, which maycause some sieve material to deteriorate, sieve material may be providedat the first end 32 that is capable of absorbing water withoutsubstantially impacting its durability and/or ability to adsorbnitrogen. In an exemplary embodiment, a first layer 36 a may be providedadjacent the first end 32 having a depth (dimension parallel to thelength of the sieve beds 12) between about ten and thirty percent of theoverall height of sieve material, such as Oxysiv 5 material. A secondlayer 36 b may then be provided that includes a high performanceadsorption material, such as Oxysiv MDX. The second layer 36 b maysubstantially fill the remainder of the sieve bed 12, as shown, or oneor more additional layers of sieve material may be provided (not shown)having desired properties. Thus, during use, when ambient air enters thefirst end 32 of the sieve bed 12, the first layer 36 a may substantiallyabsorb moisture in the air such that the second layer 36 b is exposed torelatively dry air, thereby substantially reducing the risk of damagingthe sieve material of the second layer 36 b. It has been determined forOxysiv MDX that between about 0.5-1.5 pounds, and preferably about onepound, of this sieve material per liter per minute (lpm) outletproduction provides efficient adsorption.

Although two sieve beds 12 are shown in FIGS. 1A-3, it will beappreciated that one or more sieve beds may be provided, e.g., dependingupon the desired weight, performance efficiency, and the like.Additional information on sieve beds and/or sieve materials that may beincluded in the apparatus 10 may be found in U.S. Pat. No. 4,859,217,the entire disclosure of which is expressly incorporated by referenceherein.

Returning to FIGS. 1A, 1B, and 2, the reservoir 18 may include anelongate tubular casing 70 having a lower or first end 94, which may besubstantially enclosed or open, and an upper or second end 96, which mayalso be substantially enclosed or open (e.g., if capped by a manifold orother component, as described elsewhere herein). As shown, the casing 70has an irregular hourglass shape allowing the reservoir 18 to be nestedbetween and/or adjacent to the sieve beds 12. This may minimize thespace occupied by the reservoir 18, which may help reduce the overallsize of the apparatus 10. In addition, the casing 70 may have a curvedouter wall 71 that may extend between the sieve beds 12, which mayprovide a finished outer surface for the apparatus 10, as best seen inFIGS. 1A and 1B. The casing 70 may be formed from plastic, such as ABS,polycarbonate, and the like, metal, such as aluminum, or compositematerials, similar to the other components of the apparatus 10 describedherein.

As shown in FIGS. 2 and 9A-9C, a cap 80 may be provided to at leastpartially close the upper end 96 of the casing 70. The cap 80 may besubstantially permanently or removably attached to the second ends 34 ofthe sieve beds 12 and/or the upper end 96 of the reservoir 18, e.g.,using one or more connectors, fasteners, adhesives, sonic welding, andthe like. The cap 80 may include one or more openings 82, 84 therein forallowing oxygen to flow into and out of the sieve beds 12 and/orreservoir 18, as explained further below.

Turning to FIG. 9A, the cap 80 may also include a purge orifice 81(shown in phantom), which may provide a passage communicating directlybetween the seconds ends 34 of the sieve beds 12. The purge orifice 81may remain continuously open, thereby providing a passage for oxygen topass from one sieve bed 12 to the other, e.g., while the one sieve bed12 is charging and the other is purging, as described further below. Thepurge orifice 81 may have a precisely determined cross-sectional size,e.g., between about 0.015-0.35 inch, or about 0.020 inch diameter, whichmay be based upon one or more flow or other performance criteria of thesieve beds 12, as explained further below. For example, the purgeorifice 81 may be sized such that between about two and a half and tenliters per minute (lpm) of oxygen, e.g., about five liters per minute (5lpm), flows through the purge orifice 81 in either direction at apressure differential of about five pounds per square inch (5 psi)across the purge orifice 81.

Alternatively, the purge orifice may extend between the sieve beds 12via the reservoir 18. For example, the purge orifice may include a firstpassage (not shown) extending along the cap 80 that communicates betweenthe sieve bed 12 a and the reservoir 18, and a second passage (also notshown) extending along the cap 80 that communicates between the sievebed 12 b and the reservoir 18.

Optionally, if the lower end 94 of the casing 70 is open, a cap (notshown) may also be provided for substantially closing the lower end 94of the casing 70, e.g., that may be substantially permanently orremovably attached to the lower end 94, similar to the cap 80.Alternatively, the lower end 94 of the casing 70 may be open and thelower end 94 of the casing 70 may be enclosed by a portion of the airmanifold 16, e.g., when the reservoir 18 is mounted onto or adjacent theair manifold 16, as described further below.

In a further alternative, the apparatus 10 may include multiplereservoirs (not shown) that may be provided at one or more locationswithin the apparatus 10, e.g., placed in different locations where spaceis available, yet minimizing the overall size of the apparatus 10. Thereservoirs may be connected to one another via one or more flexibletubes (not shown) and/or via the oxygen delivery manifold 102 to allowoxygen to be delivered to and withdrawn from the reservoirs. Optionally,in this alternative, one or more valves may be provided for controllingflow of oxygen into and out of the reservoirs.

In addition or alternatively, the apparatus 10 may include one or moreflexible reservoirs, e.g., bags or other containers that may expand orcontract as oxygen is delivered into or out of them. The reservoirs mayhave predetermined shapes as they expand or may expand elastically tofill available space within the apparatus 10. Optionally, one or morerigid reservoirs may be provided that communicate with one or moreflexible reservoirs (not shown), e.g., to conserve space within theapparatus 10. In further alternatives, one or more reservoirs may beprovided as portions of one or both of the air manifold 16 and theoxygen delivery manifold 102, rather than as a separate component.

Returning to FIGS. 1A, 1B, and 2, with additional reference to FIG. 5,the compressor 14 may be any device capable of drawing ambient air intothe apparatus 10 and compressing the air to one or more desiredpressures for delivery to the sieve beds 12. In the embodiment shown,the compressor 14 is a multiple headed device that includes a motor 40,a cam assembly 42 coupled to the motor 40, drive shafts or rods 44coupled to the cam assembly 40, and a plurality of diaphragm assembliesor heads 46 coupled to the drive shafts 44. The motor 40 may be abrushless DC motor, such as the Pittman 4413.

As best seen in FIG. 5, each of the diaphragm assemblies 46 includes ahousing 48, a diaphragm 50 secured to the housing 48 to define a chamber52, and a set of check valves 54 for allowing air to be drawn into andforced out of the chamber 52. The housing 48 may include one or moresubstantially rigid parts providing a support structure for thediaphragm 50 and at least partially defining the chamber 52. The housing48 may be formed from plastic, such as ABS or polycarbonate, metal, orcomposite materials, e.g., made by molding, casting, machining, and thelike.

The diaphragm 50 may be substantially permanently or removably attachedto the housing 48, e.g., using an interference fit, one or moreconnectors, fasteners adhesives, and the like (not shown), that mayprovide a substantially airtight seal between the diaphragm 50 and thehousing 48. The diaphragm 50 may be formed from flexible or semi-rigidmaterial that may be repeatedly deflected a desired distance duringoperation of the compressor 14, e.g., Ethylene Propylene Diene Monomer(“EPDM”) or “BUNA” rubber (synthetic rubber made by polymerizingbutadiene), and the like, VITON, or liquid silicone rubber (“LSR”)materials having sufficient flexibility, resiliency, and/or otherappropriate properties.

In exemplary embodiments, the housing 48 and diaphragm 50 may havesquare or rectangular cross-sections (extending into the page of FIG.5), e.g., between about one and three inches (1-3 in) on a side. Thehousing 48 may have a depth between about 0.25-1.5 inches, therebyproviding a chamber 52 defining a volume. In an exemplary embodiment,the diaphragm assemblies 46 may have a square cross-section with each ofthe height and width being about two inches (50 mm). It will beappreciated, however, that the housing 48 and diaphragm 50 may haveother cross-sectional shapes, e.g., circular, elliptical, and the like.

The diaphragm 50 may be coupled to the drive shaft 44, e.g., by a head45, such that the diaphragm 50 may move inwardly and outwardly relativeto the chamber 52 as the drive shaft 44 reciprocates along itslongitudinal axis away from and towards the cam assembly 42. Thus, thevolume of the chamber 52 may be increased and decreased as the diaphragm50 moves away from and towards the chamber 52 to draw air into thechamber 52 and force air out of the chamber 52, respectively.

Optionally, as shown in FIG. 5, the housing 48 may include one morepartitions defining passages, e.g., an inlet passage 56 _(in) and anoutlet passage 56 _(out). As explained further below, the inlet andoutlet passages 56 _(in), 56 _(out) may communicate with respectivepassages 62, 64 in the air manifold 16, e.g., via ports 57 (not shown inFIG. 5, see, e.g., FIG. 2) on the bottom of the housing 48. An inletcheck valve 54 _(in) may be provided in line with the inlet passage 56_(in), e.g., in the partition between the chamber 52 and the inletpassage 56 _(in). The inlet check valve 54 in may open when exposed to anegative pressure within the chamber 52, i.e., as the diaphragm 50 isdirected away from the chamber 52, and may close when exposed to apositive pressure within the chamber 52, i.e., as the diaphragm 50 isdirected towards the chamber 52. Similarly, an outlet check valve 54_(out) may be provided in line with the outlet passage 56 _(out) thatmay open when exposed to a positive pressure within the chamber 52 andclose when exposed to a negative pressure within the chamber 52. Thecheck valves 54 may simply be spring biased valves that open in onedirection depending upon the pressure differential across the valve,such as conventional umbrella-type valves.

During operation, the motor 40 may be continuously or selectivelyactivated to rotate a cam 43 of the cam assembly 42 and thereby causethe drive shafts 44 to reciprocate axially away from and towards the camassembly 42. For example, the cam assembly 42 may be configured suchthat the drive shafts 44 have a total axial displacement of betweenabout three and thirteen millimeters (3-13 mm). This reciprocationcauses the diaphragms 50 to move in and out relative to the housings 46,thereby drawing ambient air into the chambers 52 via the inlet passages56 _(in) and forcing compressed air out of the chambers 52 via theoutlet passages 56 _(out). The displacement of the center of thediaphragm 50 may correspond one-to-one with the displacement of thedrive shafts 44. The drive shafts 44 may change the volume of thechamber 52, e.g., by between about eighty and ninety five percent(80-95%) above and below its relaxed volume (when the diaphragm 50 issubstantially relaxed or not subjected to any forces).

In an exemplary embodiment, the reciprocal movement of the drive shafts44 is staggered or offset in time for each of the diaphragm assemblies46 a-46 c in a predetermined pattern, e.g., based upon the configurationof the cam 43 of the cam assembly 42. Thus, compressed air may begenerated sequentially by each of the heads 46. This may also minimizethe amount of vibration or noise generated by the compressor 14, e.g.,such that vibration or movement of one of the diaphragm assemblies 46 atleast partially offsets the others. Additional information regardingoperation and control of the compressor 14 is provided below.

In addition, because the diaphragm assemblies may be angularly offsetfrom one another, e.g., by one hundred twenty degrees (120°) whendisposed symmetrically about the cam assembly 42, this may also offsetor minimize vibrations created during operation of the compressor 14. Bycomparison, in an alternative embodiment, two diaphragm assemblies (notshown) may be provided on opposite sides of the cam assembly in a linearconfiguration defining an axis, although this a configuration mayincrease vibrations along the axis.

Alternatively, more than three (3) heads may be provided, although thismay increase the cost and/or complexity of operation of the apparatus10. In order to minimize vibration, it may be desirable to provide anodd number of diaphragm assemblies (e.g., three, five, seven, etc.),e.g., in a symmetrical spoke configuration that does not create a linearaxis between any of the diaphragm assemblies, which may at leastpartially offset vibrations between the various heads.

Turning to FIGS. 2 and 5A-6B, the lower or air manifold 16 generallyincludes one or more substantially planar structures defining aplurality of passages 62-68 therein. Generally, the air manifold 16 issealed such that the passages 62-68 are substantially airtight otherthan at openings 72-79, 86-90. The openings 72-79, 86-90 may allow othercomponents, e.g., the compressor 14, the sieve beds 18, and air controlvalves 20, to communicate with the passages 62-68 for moving air throughthe air manifold 16 in a desired manner, as explained further below.Optionally, the air manifold 16 may include one or more holes, pockets,and the like for receiving mounts, connectors, and/or fasteners (notshown), e.g., for attaching components of the apparatus 10 to the airmanifold 16, e.g., the sieve beds 12, the compressor 14, reservoir 18,and/or air control valves 20.

The air manifold 16 may be substantially rigid, e.g., thereby providingor enhancing a structural integrity of the apparatus 10. In oneembodiment, the air manifold 16 may define one or more outer structuralsurfaces for the apparatus 10, e.g., a lower or bottom surface of theapparatus 10, thereby eliminating the need for an additional lowerexterior skin. The air manifold 16 may be formed from any engineeringgrade material, e.g., plastic, such as ABS, polycarbonate, and the like;metal, such as aluminum, and the like; or composite materials. The airmanifold 16 may be formed by injection molding, casting, machining, andthe like.

In an exemplary embodiment, the air manifold 16 may be formed fromrelatively lightweight plastic material, e.g., such that the airmanifold 16 weighs not more than about 0.25-4.0 pounds. Alternatively,all or one or more portions of the air manifold 16 may be formed fromresilient semi-rigid or flexible material, e.g., to increase thedurability and/or shock resistance of the apparatus 10.

In the embodiment shown, the air manifold 16 includes a manifold base 58including a plurality of channels therein that at least partially definethe passages 62-68, and a manifold cap 60 that mates with the manifoldbase 58 to substantially enclose the channels to further define thepassages 62-68. It will be appreciated that the air manifold 16 may beformed from one or more components, instead of the manifold base 58 andthe manifold cap 60, that mate together or otherwise cooperate to definethe passages 62-68 described herein.

As best seen in FIG. 6, the manifold base 58 may include channels thatat least partially define one or more compressor inlet passages 62,compressor outlet passages 64, sieve bed passages 66, and exhaustpassages 68. Portions of the manifold base 58 unnecessary to define thepassages 62-68 and/or mounting surfaces may be omitted, e.g., to reducethe overall weight of air the manifold 16 without substantiallyimpacting its structural integrity. Alternatively, the manifold base 58may have a substantially continuous lower wall, e.g., which may besubstantially smooth and/or may include legs or other components (notshown) upon which the apparatus 10 may be set.

In addition or alternatively, the manifold base 58 may include at leasta portion of a side wall 59, e.g., which may define another outerstructural surface of the apparatus 10. In a further alternative, asshown in FIG. 2, the side wall 59 may be part of the manifold cap 60,rather than the manifold base 58. In yet another alternative, the airmanifold 16 may be relatively flat (rather than “L” shaped), and theside wall may be a separate component (not shown) that may be connectedor otherwise attached to the air manifold 16.

Turning to FIGS. 7A and 7B, the manifold cap 60 may include one or morechannels that mate with the channels in the manifold base 58 to furtherdefine the passages 62-68, e.g., the compressor inlet passages 62,compressor outlet passages 64, sieve bed passages 66, and exhaustpassages 68. Alternatively, the channels in the manifold cap 60 may beslightly larger or smaller than the channels in the manifold base 58such that the channel walls overlap, which may enhance the connectionbetween the manifold cap 60 and the manifold base 58. In anotheralternative, the manifold cap 60 may have a substantially smooth lowersurface that mates against the channel walls and/or other components ofthe manifold base 58 to further define the passages 62-68.

The manifold cap 60 may be attached to the manifold base 58 using one ormore connectors, e.g., cooperating detents, such as tabs andcorresponding grooves, or fasteners, such as screws, rivets, bolts, andthe like. In addition or alternatively, the manifold cap 60 may beattached to the manifold base 58 using adhesives, sonic welding, and thelike, e.g., along one or more contact surfaces between the manifold base58 and the manifold cap 60.

With continued reference to FIGS. 7A and 7B, the manifold cap 60 mayinclude a plurality of openings 72-79, 86-90 that communicate with thepassages 62-68. For example, the manifold cap 60 may include an airinlet port 79 that communicates with the compressor inlet passage 62.The inlet port 79 may be coupled to a tube or other hollow structure(not shown) extending to an inlet opening 160 (not shown, see FIG. 2) inan outer surface of the apparatus 10, e.g., to allow ambient air to bedrawn into the apparatus 10. Optionally, as shown in FIG. 3, an inletair filter 162 may be provided in line before the inlet port 79 toremove dust or other particles from the ambient air drawn into the inletopening 160 before it enters the compressor 14.

In addition, returning to FIGS. 7A and 7B, the manifold cap 60 mayinclude multiple pairs of openings 72, 74 for communicating with thecompressor 14. In the embodiment shown, the manifold cap 60 includesthree pairs of openings 72, 74 corresponding to ports 57 (not shown, seeFIG. 2) on the three diaphragm assemblies 46 of the compressor 14. Eachpair of openings 72, 74 may be spaced apart a predetermined distancesimilar to the spacing of the ports 57 on the diaphragm assemblies 46.One or both of the openings 72, 74 and the ports 57 may include nipplesor other extensions to facilitate a substantially airtight connectionbetween the diaphragm assemblies 46 and the manifold cap 60. The ports57 may be connected to the openings 72, 74, e.g., by one or more ofinterference fit, mating threads, cooperating detents, adhesives, andthe like.

When the compressor 14 is mounted to or adjacent the air manifold 16,the inlet passages 56 _(in) of the diaphragm assemblies 46 maycommunicate with the openings 72, and consequently with the compressorinlet passage 62. During use, when each of the diaphragm assemblies 46,in turn, draws in outside air via the inlet passages 56 _(in) air may bedrawn through the respective openings 72, the compressor inlet passage62, and the inlet port 79. Similarly, the outlet passages 56 _(out) ofthe diaphragm assemblies 46 may communicate with the openings 74, andconsequently with the compressor outlet passage 64. During use, wheneach of the diaphragm assemblies 46 delivers compressed air out theoutlet passages 56 _(out), the compressed air may enter the respectiveopenings 74 into the compressor outlet passages 64 in the air manifold16.

With continued reference to FIGS. 7A and 7B, the manifold cap 60 mayalso include a plurality of air control valve openings 86, 88 adjacentone another that overly the compressor outlet passage 64, the sieve bedpassages 66, and/or the exhaust passage 68. Thus, when the manifold cap60 is attached to the manifold base 58, the air control valve openings86, 88 may communicate with respective passages 64-68. In particular,supply valve inlet openings 86 _(in) may communicate with the compressoroutlet passage 64, while exhaust valve inlet openings 88 _(in)communicate with respective sieve bed passages 68. Supply valve outletopenings 86 _(out) may communicate with respective sieve bed passages66, while exhaust valve outlet openings 88 _(out) communicate with theexhaust passage 68.

The manifold cap 60 may also include sieve bed openings 90 thatcommunicate with enlarged portions of the sieve bed passages 66. Thus,the sieve bed openings 90 may communicate with the first ends 32 ofrespective sieve beds 12 when the sieve beds 12 are mounted to oradjacent the air manifold 16. Further, as best seen in FIG. 7B, themanifold cap 60 may also include one or more exhaust openings 92 thatcommunicates with the exhaust passage 68.

Optionally, a tube, nozzle, or other device (not shown) may be coupledto the exhaust opening(s) 92 to direct exhaust air (generallyconcentrated nitrogen) from the sieve beds 12, as explained furtherbelow. In one embodiment, the exhaust air may be directed towards thecontroller 22 or other electronics within the apparatus 10, e.g., forcooling the electronics. Using concentrated nitrogen as a cooling fluidfor the internal electronics may provide a safety feature for theapparatus 10, namely reducing the risk of fire if the electronics everoverheat or short. Since most of the oxygen has been removed from theexhaust air, there is little or no fuel in the exhaust air to support afire. Further, with the exhaust air being directed into the interior ofthe apparatus 10, if the reservoir 18 or sieve beds 12 were ever todevelop a leak communicating with the interior of the apparatus 10, theresulting gas mixture would have no more oxygen (as a percentage ofvolume) than ambient air.

As described further below, the air control valves 20 may be mounted tothe manifold cap 60 over the valve openings 86, 88 and the air controlvalves 20 may be selectively opened and closed to provide flow paths,e.g., from the compressor outlet passage 64 to the sieve bed passages 66and/or from the sieve bed passages 66 to the exhaust passage 68. Forexample, with additional reference to FIG. 3, when supply air controlvalve 20 a _(S) is open, a flow path may defined from the compressor 14through openings 72, compressor passage 62, supply inlet openings 86_(in), the air control valve 20 a _(S) supply outlet opening 86 _(out),and the sieve bed passage 66 a, into the sieve bed 12 a. When exhaustair control valve 20 b _(E) is open, a flow path may be defined from thesieve bed 12 b, through the sieve bed passage 66 b, exhaust inletopenings 88 _(in), the air control valve 20 b _(E), exhaust outletopenings 88 _(out), exhaust passage 68, and out exhaust opening(s) 92.

The air manifold 16 may replace a plurality of tubes and valves thatwould otherwise be necessary to deliver air to and from the sieve beds12. Because these individual tubes and valves are eliminated andreplaced with a simple manifold including not more than four air controlvalves 20, the air manifold 16 may reduce the overall size, weight,and/or cost of the apparatus 10, which may be useful, particularly inorder to make the apparatus 10 convenient, easy to use, and/orinexpensive.

In addition, the air manifold 16 may facilitate modifications, e.g., toreduce pressure losses and/or dampen noise. For example, to minimizeenergy needs for the apparatus 10, the size and/or shape of the passages62-68 may be designed to reduce losses as compressed air pass throughthe passages 62-68. It has been found that if the pressure lossincreases by one pound per square inch (1 psi), it may increase powerconsumption of the apparatus 10 by as much as ten percent (10%) or more.FIG. 10 shows pressure losses that may be encountered during threeexemplary average flow rates, i.e., twenty four (24), thirty (30) andfifty (50) liters per minute (lpm). As the average flow diameter of thepassages 62-68 is increased, the pressure drop is reduced significantly.Thus, it may be desirable for the passages 62-68 to have a size of atleast about 0.25 inch diameter or other equivalent cross-section.

In addition, the air manifold 16 may facilitate providing baffles orother sound dampening devices or materials within the flow paths of theair moving through the apparatus 10. For example, one or more baffles,venturis, flow modifiers, and the like (not shown) may be moldeddirectly into the channels of the manifold base 58 to absorb sound wavesor reduce noise generated by airflow. Alternatively, such components maybe inserted or mounted within the channels before the manifold cap 60 isattached to the manifold base 58. In yet another alternative, the airmanifold 16 may allow flow control valves to be mounted directly in oneor more of the passages 62-68.

Returning to FIGS. 1A-3, the air control valves 20 may be mounted orotherwise attached to the air manifold 16, e.g., to the manifold cap 60.In the embodiment shown, four “two way” air control valves 20 may beprovided that may be mounted to the manifold cap 60, e.g., using one ormore connectors, fasteners, adhesives, and the like. As explainedfurther below, four air control valves 20 allow each sieve bed 12 to bepressurized and/or exhausted independently of the other, optionally withthe ability to overlap the pressurization cycles.

An exemplary two-way valve that may be used for each of valves 20 is theSMC DXT valve, available from SMC Corporation of America, ofIndianapolis, Ind. This valve is a relatively small plastic pilotoperated diaphragm valve. Because of the large diaphragm area, it has avery low minimum operating pressure, which may be particularly usefulgiven the operating pressures of the apparatus 10 during use. The valvemay be provided as “normally open.” When pressure is applied to the topside of the diaphragm through the pilot valve, the diaphragm may beforced down onto a seat, shutting off the flow. Either a normally openor normally closed pilot solenoid valve may be used. Since the diaphragmvalve itself is normally open, using a normally open solenoid valve maycreate normally closed overall operation, requiring application ofelectrical energy to open the valve.

Alternatively, the air control valves 20 may be replaced with two“three-way” valves, which may require some minor changes to the openingsand/or passages in the air manifold 16. Such valves, however, may bemore expensive, complicated to operate, and/or may require greaterpressure to pilot than the pressures encountered during use of theapparatus 10. In further alternatives, one or more other multipleposition valves may be provided, instead of the four two way valves.

Returning to FIG. 3, the four air control valves 20 may be provided on asingle valve manifold 21, e.g., an aluminum manifold, and the ports maybe threaded inlet and outlet ports provided separately or as part of thevalve manifold 21. After assembling the air control valves 20 to thevalve manifold 21, the valve manifold 21 may be mounted to the airmanifold 16 over the openings 86, 88. Alternatively, the individual aircontrol valves 20 may be mounted directly to the air manifold 16, e.g.,to avoid the valve manifold 21 or any other fittings and/or tubing,which may further reduce the overall size and/or weight of the apparatus10.

Returning to FIGS. 1A, 1B, and 2, with additional reference to FIGS.8A-8B, the upper or oxygen delivery manifold 102 may be provided fordelivering oxygen stored in the reservoir 18 to a user of the apparatus10. Similar to the air manifold 16, the oxygen delivery manifold 102 mayprovide sufficient structural integrity to provide an outer structuralsurface of the apparatus 10, e.g., thereby eliminating the need for aseparate outer or upper skin for the apparatus 10. The oxygen deliverymanifold 102 may be manufactured and assembled using similar materialsand/or methods to the air manifold 16, described above.

Optionally, as shown in FIG. 8B, the oxygen delivery manifold 102 mayinclude one or more ribs or other reinforcing structures 103, e.g., on alower surface of the oxygen delivery manifold 102. The reinforcingstructures 103, may be molded or otherwise formed directly in the oxygendelivery manifold 102 in a desired pattern or attached to the oxygendelivery manifold 102, e.g., overlying the sieve beds 12 (not shown inFIG. 5B). Such reinforcing structures 103 may reinforce the oxygendelivery manifold 102, e.g., from the biasing mechanism 39 within thesieve beds 12 and/or against the pressure of the air within the sievebeds 12, which may apply an upward force against the oxygen supplymanifold 102.

In the embodiment shown in FIG. 2, the oxygen delivery manifold 102includes a manifold base 104 at least partially defining one or moreoxygen delivery passages 108, 109 and a manifold cap 106 furtherdefining the oxygen delivery passages 108, 109. The oxygen deliverypassages 108, 109 may be disposed adjacent one another in the manifoldbase 104 and include a plurality of openings 126-138 for communicatingwith other components related to delivering oxygen to a user of theapparatus 10, as explained further below. The manifold base 104 may alsoinclude one or more battery openings 140 and/or an interface window 142,which may be molded or otherwise formed therein.

Optionally, as shown in FIG. 2, the manifold base 104 of the oxygendelivery manifold 102 may include at least a portion of a side panel 159of the apparatus 10. The side panel 159 may abut, interlock, orotherwise mate with the side panel 59 on the air manifold 16. The sidepanels 59, 159 may provide an outer structural wall for the apparatus 10that is substantially rigid. Thus, the side panels 59, 159 the manifolds16, 102, and the sieve beds 12 and/or reservoir 18 combined may providethe necessary structural frame to support the apparatus 10 and itsinternal components, as explained further below. Alternatively, one orboth side panels 59, 159 may be provided as a separate panel (not shown)that may be connected or otherwise attached to the air manifold 16and/or the oxygen delivery manifold 102.

Returning to FIG. 2, the side panel 159 may include one or more inletopenings 160 that may communicate with an interior of the apparatus 10.As shown, the side panel 159 includes two inlet openings or screens 160adjacent one another. The inlet openings 160 may be provided in adesired array, e.g., in a rectangular, square, round, or otherconfiguration. In an exemplary embodiment, each of the inlet openings160 may have a height and/or width of between about one and two inches(25-50 mm). The inlet openings 160 may include relatively small holes,e.g., between about 0.025-0.15 inch (0.6-4 mm) diameter, allowing air topass easily through the inlet openings 160, yet preventing large objectsfrom passing therethrough.

For example, the first inlet opening 160 a may provide an inlet fordrawing air into the compressor 14, e.g., via tubing and the like (notshown) communicating with the air inlet port 79 of the air manifold 16,as described above. The second inlet opening 160 b may provide aventilation inlet for ambient air to be drawn into the interior of theapparatus 10, e.g., to assist cooling the internal electronics and/orthe sieve beds 12. An intake fan 164 may be mounted adjacent the secondinlet opening 160 b, e.g., to draw ambient air into the interior of theapparatus 10 at a constant or variable speed and/or volume.

Optionally, the apparatus 10 may include one or more gaps, e.g.,vertical spaces between the sieve beds 12 and/or reservoir 18 (notshown), to allow air to escape from the interior of the apparatus 10.For example, it may be desirable to have air within the interior of theapparatus 10 (particularly, the exhaust gas from the exhaust opening(s)92) escape the apparatus 10 on the opposite end from the inlet openings160 to avoid drawing nitrogen-rich air back into the sieve beds 12,which would reduce the efficiency, and possibly effectiveness, of theapparatus 10. Alternatively, one or more outlet openings (not shown) maybe provided on the apparatus 10, e.g., in the air manifold 16, theoxygen delivery manifold 102, and/or one or more side panels (not shown)to allow air to escape from within the interior of the apparatus 10 in adesired manner.

Returning to FIG. 2, the apparatus 10 may include one or more componentsrelated to delivering oxygen from the reservoir 18 to a user. Thesecomponents may be attached or otherwise mounted to or adjacent theoxygen delivery manifold 102, e.g., using methods similar to the methodsfor attaching other components of the apparatus 10 described herein.

For example, a pair of check valves 110 may be provided in the manifoldbase 104 that overly openings 82 in the cap 80. The check valves 110 maysimply be pressure-activated valves, similar to the check valves 54described above. When the oxygen delivery manifold 102 is mounted to oradjacent the sieve beds 12 and the reservoir 18, the check valves 110provide one-way flow paths from the sieve beds 12 into the oxygendelivery passage 108. The oxygen delivery passage 108 communicatesdirectly and continuously with the reservoir 18 via opening 112.

A pressure sensor 114 may be provided within the reservoir 18 orcommunicating with the oxygen delivery passage 108. The pressure sensor114 may detect absolute pressure within the reservoir 18, and,consequently, within the oxygen delivery passage 108. In addition,because of the check valves 110, the pressure sensor 114 may provide areading of the maximum pressure within the sieve beds 12. Specifically,because the check valves 110 allow one-way flow of oxygen from the sievebeds 12 into the reservoir 18 and oxygen delivery passage 108, wheneverthe pressure in either sieve bed 12 exceeds the pressure in thereservoir 18, the respective check valve 110 may open. Once the pressurewithin either sieve bed 12 becomes equal to or less than the pressure inthe reservoir 18, the respective check valve 110 may close.

In addition, as shown in FIGS. 2 and 3, an oxygen delivery valve 116,oxygen sensor 118, one or more pressure sensors 120, 122, and one ormore air filters 124 may be provided in line with the oxygen deliverypassages 108, 109, e.g., mounted to the oxygen delivery manifold 102.For example, with additional reference to FIGS. 8A and 8B, the manifoldbase 104 may include oxygen control valve openings 126, pressure sensoropenings 128, 138, oxygen sensor openings 130, 132, and outlet openings134, 136 for communicating with these components.

The oxygen delivery valve 116 may be mounted to the oxygen deliverymanifold 102, e.g., below the oxygen control valve openings 126, forcontrolling the flow of oxygen between the oxygen delivery passages 108and 109, and consequently from the reservoir 18 out of the apparatus 10to a user. The oxygen delivery valve 116 may be a solenoid valve coupledto the controller 22 that may be selectively opened and closed. Anexemplary valve that may be used for the oxygen delivery valve 116 isthe Hargraves Technology Model 45M, which may have a relatively largeorifice size, thereby maximizing the possible flow through the oxygendelivery valve 116. Alternatively, it may also be possible to use aParker Pneutronics V Squared or Series 11 valve.

When the oxygen delivery valve 116 is open, oxygen may flow from oxygendelivery passage 108, through the oxygen control valve openings 126 a,126 b, the oxygen delivery valve 116, the oxygen control valve opening126 c, and into oxygen delivery passage 109. The oxygen delivery valve116 may be opened for desired durations at desired frequencies, whichmay be varied by the controller 22, thereby providing pulse delivery asexplained further below. Alternatively, the controller 22 may maintainthe oxygen delivery valve 116 open to provide continuous delivery,rather than pulsed delivery. In this alternative, the controller 22 maythrottle the oxygen delivery valve 116 to adjust the volumetric flowrate to the user.

The pressure sensor 120 may also be mounted to and/or below the oxygendelivery manifold 102 such that ports of the pressure sensor 120 arecoupled to or otherwise communicate with the pressure sensor openings128. Thus, the ports of the pressure sensor 120 may measure a pressuredifference between oxygen delivery passages 108, 109, and consequentlyacross the oxygen delivery valve 116. Optionally, the pressure sensor120 may be used to obtain reservoir pressure, and pressure sensor 114may be eliminated. For example, when the oxygen delivery valve 116 isclosed, pressure upstream of the oxygen delivery valve 116 maycorrespond substantially to the pressure within the reservoir 18.

The pressure sensor 120 may be coupled to the controller 22, e.g., toprovide signals that may be processed by the controller 22 to determinethe pressure differential across the oxygen delivery valve 116. Thecontroller 22 may use this pressure differential to determine a flowrate of the oxygen being delivered from the apparatus 10 or otherparameters of oxygen being delivered. The controller 22 may change thefrequency and/or duration that the oxygen delivery valve 116 is openbased upon the resulting flow rates, e.g., based upon one or morefeedback parameters, as described further below.

The oxygen sensor 118 may also be mounted to and/or below the oxygendelivery manifold 102 such that ports on the oxygen sensor 118communicate with the oxygen sensor openings 130, 132. The oxygen sensor118 may be capable of measuring the purity of oxygen passingtherethrough, e.g., an ultrasonic sensor that measures the speed ofsound of the gas passing through the oxygen sensor 118, such as thosemade by Douglas Scientific of Shawnee, Kans. Alternatively, the oxygensensor 118 may be a ceramic or sidestream sensor. Ultrasonic sensors mayuse less power than ceramic sensors, e.g., about fifty milliwatts (50mW) versus one watt (1 W)), but may be more expensive.

The oxygen sensor 118 may be coupled to the controller 22 and maygenerate electrical signals proportional to the purity that may beprocessed by the controller 22 and used to change operation of theapparatus 10, as described further below. Because the accuracy of theoxygen sensor 118 may be affected by airflow therethrough, it may bedesirable to sample the purity signals during no flow conditions, e.g.,when the oxygen delivery valve 116 is closed.

The pressure sensor 122 may be mounted to and/or or below the oxygenmanifold 102 such that the port of the pressure sensor 122 communicateswith pressure sensor opening 138. The pressure sensor 122 may be a piezoresistive pressure sensor capable of measuring absolute pressure.Exemplary transducers that may be used include the Honeywell Microswitch24PC01SMT Transducer, the Sensym SX01, Motorola MOX, or others made byAll Sensors. Because the pressure sensor 122 may be exposed to the fullsystem pressure of the apparatus 10, it may be desirable for theover-pressure rating of the pressure sensor 122 to exceed the fullsystem pressure, e.g., to be at least about fifteen pounds per squareinch (15 psi).

The pressure sensor 122 may be coupled to the controller 22 forproviding signals proportional to the pressure detected by the pressuresensor 122, as explained further below. Because the pressure sensor 122may not have a zero reference, the pressure signals from the pressuresensor 122 may drift during operation of the apparatus 10. To minimizeany drift or other error introduced by the pressure sensor 122, a smallvalve (not shown) may be coupled to the pressure sensor 122 toperiodically vent or zero the pressure sensor 122, e.g., when the oxygendelivery valve 116 is open and delivering oxygen.

Alternatively, a relative small orifice (e.g., about 0.010 inchdiameter) may be provided in the line between the oxygen delivery valve116 (e.g., the normally open port), and the pressure sensor 122. Thisorifice may be small enough not to adversely affect the pressure signalsfrom the pressure sensor 122, but large enough so that the pressuresensor 122 is bled to zero, e.g., during a pulse as short as one hundredmilliseconds (100 ms.). Additional information on using such an orificemay be found in published application No. 2003/0150455, the entiredisclosure of which is expressly incorporated by reference herein. Inanother alternative, the controller 22 may implement a filteringalgorithm to recognize the beginning of the user's breath.

The manifold base 104 may include a recess 133 that communicates withoxygen sensor opening 132 and pressure sensor opening 138. A cover orother member (not shown) may be attached over or otherwise cover therecess 133, e.g., to provide a substantially airtight passage defined bythe recess 133. Thus, the pressure sensor 122 may measure an absolutepressure of the oxygen within the recess 133. This pressure reading maybe used to detect when a user is beginning to inhale, e.g., based upon aresulting pressure drop within the recess 133, which may triggerdelivering a pulse of oxygen to the user, as explained further below.

The air filter 124 may be mounted to or adjacent the oxygen deliverymanifold 102, and may include any conventional filter media for removingundesired particles from oxygen being delivered to the user. As bestseen in FIG. 8A, the oxygen delivery manifold 102 may include a recess137 shaped to receive the air filter 124 therein. The air filter 124 maybe secured within the recess 137 by an interference fit, by one or moreconnectors, adhesives, and the like.

The recess 137 (shown in FIG. 8A) may communicate with the channel 135(shown in FIG. 8B) via outlet opening 136. In the embodiment shown, thechannel 135 extends between the outlet openings 134, 136 formed in andthrough the manifold base 104. A cover or other member (not shown) maybe attached or otherwise cover the channel 135, e.g., to provide asubstantially airtight passage defined by the channel 135. Thus, oxygendelivered from the oxygen sensor 118 may leave the recess 133 throughoutlet opening 134, pass along channel 135, and enter recess 137 throughoutlet opening 136. The oxygen may then pass through the air filter 124and be delivered to the user.

Optionally, a dome or other device (not shown) may be mounted to theoxygen delivery manifold 102 over the recess 137. The dome may beattached to the oxygen delivery manifold 102, e.g., by mating threads,one or more detents or other connectors, adhesives, and the like (alsonot shown). The dome may include a nipple or other connector to which acannula, e.g., flexible hose, and the like (also not shown), may beattached for delivering the oxygen to a user, as is known in the art.The dome may be separate from the air filter 124 or the dome and airfilter 124 may be a single assembly that may be attached together to theoxygen delivery manifold 102 over the recess 137.

It will be appreciated that other configurations and/or components maybe provided for delivering oxygen to the user, rather than the oxygendelivery manifold 102 and the components attached thereto describedabove. In addition, although the components, e.g., oxygen delivery valve116, pressure sensors 120, 122, oxygen sensor 118, and air filter 124are described in a particular sequence (relative to oxygen flowingthrough the oxygen delivery manifold 102), the sequence of thesecomponents may be changed, if desired.

Returning to FIG. 2, the controller 22 may include one or more hardwarecomponents and/or software modules that control one or more aspects ofthe operation of the apparatus 10. The controller 22 may be coupled toone or more components of the apparatus 10, e.g., the compressor 14, theair control valves 20, the oxygen delivery valve 116, the pressuresensors 114, 120, 122, and/or the oxygen sensor 118. The components maybe coupled by one or more wires or other electrical leads (not shown forsimplicity) capable of receiving and/or transmitting signals between thecontroller 22 and the components.

The controller 22 may also be coupled to a user interface 144, which mayinclude one or more displays and/or input devices. In the embodimentshown in FIG. 2, the user interface 144 may be a touch-screen displaythat may be mounted within or below interface window 142 in the oxygendelivery manifold 102. The user interface 144 may display informationregarding parameters related to the operation of the apparatus 10 and/orallow the user to change the parameters, e.g., turn the apparatus 10 onand off, change dose setting or desired flow rate, etc., as explainedfurther below. Although a single user interface 144 is shown, it will beappreciated that the user interface may include multiple displays and/orinput devices, e.g., on/off switches, dials, buttons, and the like (notshown). The user interface 144 may be coupled to the controller 22 byone or more wires and/or other electrical leads (not shown forsimplicity), similar to the other components.

For simplicity, the controller 22 shown in FIG. 2 includes a singleelectrical circuit board that includes a plurality of electricalcomponents thereon. These components may include one or more processors,memory, switches, fans, battery chargers, and the like (not shown)mounted to the circuit board. It will be appreciated that the controller22 may be provided as multiple subcontrollers that control differentaspects of the operation of the apparatus 10. For example, a firstsubcontroller may control operation of the motor 40 of the compressor 14and the air control valves 20, and a second subcontroller may controloperation of the oxygen delivery valve 116 and/or the user interface144.

The controller 22, e.g., a first subcontroller that controls operationof the compressor 14, may include a brushless DC motor controller, suchas one of the Motorola/ON MC33035 family, the Texas Instruments DSP TMS320LF240, and/or the MSP 430 F449IPZ. Such a controller may use utilizehall sensors (not shown) in the motor 40 to time commutation.Alternatively, a sensor-less controller may be used that allowscommutation timing via back-EMF measurement, i.e., the position of thearmature of the motor may be determined by the measurement of the backEMF of the coils of the motor. This alternative may be less expensive,because the sensors in the motor may be eliminated, and the wiring tothe motor may be simplified. For example, Fairchild may have a dedicatedintegrated circuit appropriate for use in the controller 22.Alternatively, a Texas Instruments DSP TMS 320LF240 or the MSP 430F4491PZ microprocessor may be used that includes integrated sensor-lesscontrol peripherals.

The first subcontroller (or other component of the controller 22) maycontrol a speed of the motor, and consequently, a pressure and/or flowrate of compressed air delivered by the diaphragm assemblies 46. Thecontroller 22 may also control the sequence of opening and closing theair control valves 20, e.g., to charge and purge the sieve beds 12 in adesired manner, such as the exemplary methods described further below.

The second subcontroller (or other component of the controller 22) maycontrol the oxygen delivery valve 116, e.g., to deliver oxygen from thereservoir 18 to a user based upon pressure signals received from thepressure sensor 122. The second subcontroller may also receive inputinstructions from the user and/or display information on the userinterface 144. In addition, the subcontrollers or other components ofthe controller 22 may share information in a desired manner, asdescribed below. Thus, the controller 22 may include one or morecomponents, whose functionality may be interchanged with othercomponents, and the controller 22 should not be limited to the specificexamples described herein.

In addition, the apparatus 10 may include one or more power sources,coupled to the controller 22, compressor 14, the air control valves 20,and/or the oxygen delivery valve 116. For example, as shown in FIG. 2, apair of batteries 148 may be provided that may be mounted or otherwisesecured to the air manifold 16, e.g., along the open sides between theside walls 59, 159 and the sieve beds 12. The air manifold 16 mayinclude one or more mounts 149 that may be received in the batteries148, e.g., to stabilize and/or otherwise secure the batteries 148vertically within the apparatus 10. In addition or alternatively, otherstraps or supports (not shown) may also be used to secure the batteries148 within the apparatus 10.

In exemplary embodiments, the batteries 148 may be rechargeablebatteries, such as eleven (11) volt nominal 3 series Li-Ion batteries, 4series Li-Ion batteries (such as those available from Inspired Energy,e.g., Part No. NL2024), and the like. For 3 series packs, standard onepound (1 lb) packs may have a current limitation of three (3) amperes,while one and a half pound (1.5 lb.) packs may have a maximum current ofsix (6) amperes. Additional information on Inspired Energy batteriesthat may be used may be found at www.inspired-energy.com. Other sourcesof batteries may include Molien Energy (www.molienergy.com), GPBatteries (www.gpbatteries.com), Micro-Power (www.micro-power.com), andBuchmann (www.buchmann.ca).

The controller 22 may control distribution of power from the batteries148 to other components within the apparatus 10. For example, thecontroller 22 may draw power from one of the batteries 148 until itspower is reduced to a predetermined level, whereupon the controller 22may automatically switch to the other of the batteries 148.

Optionally, the apparatus 10 may include an adapter such that anexternal power source, e.g., a conventional AC power source, such as awall outlet, or a portable AC or DC power source, such as an automotivelighter outlet, a solar panel device, and the like (not shown). Anytransformers or other components (also not shown) necessary to convertsuch external electrical energy such that it may be used by theapparatus 10 may be provided within the apparatus 10, in the cablesconnecting the apparatus 10 to the external power source, or in theexternal device itself.

Optionally, the controller 22 may direct some electrical energy fromexternal sources back to the batteries 148 to recharge them in aconventional manner. The controller 22 may also display the status ofthe electrical energy of the apparatus 10, e.g., automatically or uponbeing prompted via the user interface 144, such as the power level ofthe batteries 148, whether the apparatus 10 is connected to an externalpower source, and the like.

The controller 22 may include one or more dedicated components forperforming one or more of these functions. An exemplary batterymanagement integrated circuit (IC) that may be included in thecontroller 22 is the Maxim MAX1773 type, which is designed for dualbattery systems (see, e.g., www.maximic.com/quick_view2.cfm/qv_pk/2374for more information). Another is the Linear LTC1760, which is alsodesigned for dual battery systems and combines similar selectorfunctions with charging (see, e.g.,www.linear.com/prod/datasheet.html?datasheet=989 for more information).

Returning to FIGS. 1A-3, to assemble the apparatus 10, the components ofthe air and oxygen delivery manifolds 16, 102 may be manufactured andassembled, as described above. For example, the manifold bases 58, 104,manifold caps 60, 106 and/or other caps or covers (not shown) may bemolded or otherwise manufactured, and the manifold caps 60, 106 and/orother caps or covers (not shown) may be attached to the manifold bases58, 104, e.g., using one or more of cooperating detents, connectors,fasteners, interference fit, adhesives, and the like (not shown).Similarly, the sieve beds 12, reservoir 18, and compressor 20 may bemanufactured and/or assembled, e.g., as described above.

The air control valves 16, sieve beds 12, reservoir 18, and/orcompressor 20 may be mounted to the air manifold 16, e.g., to themanifold cap 60, also as described above. Similarly, the oxygen deliveryvalve 116, pressure sensors 120, 122, oxygen sensor 118, air filter 124,and/or other components may be mounted to oxygen delivery manifold 102.The oxygen delivery manifold 102 may be attached to the sieve beds 12and reservoir 18, e.g., after or before the sieve beds 12 and reservoir18 are attached to the air manifold 16. The order of assembly is notimportant and may be changed to facilitate desired manufacturingfacilities and/or procedures.

Simultaneously or separately, the side walls 59, 159 may be attached toone another, or, if the side walls 59, 159 are one or more separatepanels (not shown), they may be attached to and/or between the airmanifold 16 and the oxygen delivery manifold 102. The resultingstructure may provide a structural frame for the apparatus 10 that mayeliminate the need for additional supports or structural or cosmeticouter skins.

The controller 22 may be mounted within the structural frame and anywires or other leads may be connected between the controller 22 and theother components coupled thereto. In an exemplary embodiment, thecontroller 22 (or at least one subcontroller) may be mounted to the airmanifold 16, e.g., vertically adjacent the exhaust opening(s) 92. Thus,the gas exiting the air manifold 16, e.g., concentrated nitrogen, may bedirected across or otherwise towards the controller 22 for cooling itscomponents. Brackets or other supports (not shown) may be mounted to themanifold cap 60 and the circuit board(s) and/or other components of thecontroller 22 may be secured by the brackets or supports in aconventional manner.

The batteries 148 may be inserted into the apparatus 10 at any time,e.g., after access to the interior is no longer needed. The side regionsbetween the manifolds 16, 102 may remain substantially open (other thanany area covered by the batteries 148), e.g., to provide access duringassembly and/or testing of the components of the apparatus 10.Optionally, a relatively thin and/or light-weight skin or otherstructure (not shown) may be provided in each of the open side regionsto substantially enclose the interior of the apparatus 10, e.g., tolimit access and/or protect the components therein.

To provide a water-tight and/or aesthetic finish for the apparatus 10, acase (not shown) may be provided into which the entire apparatus 10 maybe placed. Conventional portable oxygen concentrator devices, despitehaving a structural outer skin, are often kept in a carrying case, e.g.,constructed from canvas, fabric, plastic, or combinations of these orother materials. Unlike such devices, the apparatus 10 may be providedin a relatively soft bag or other case without additional rigidstructural skins or panels, which may reduce the overall weight of theapparatus 10.

An exemplary embodiment of a case may include one or more closableopenings, e.g., overlying the battery openings 142, the filter recess137, and/or other locations on the apparatus 10. In addition, the casemay include an opening or a substantially transparent window that may beprovided over the user interface 144. Optionally, the case may includepadding or other sound absorption and/or cushioning materials in one ormore panels of the case.

Returning to FIG. 3, the basic operation of the apparatus 10 will now bedescribed. Generally, operation of the apparatus 10 has two aspects,concentrating oxygen from ambient air by adsorption within the sievebeds 12, and delivering concentrated oxygen to a user from the reservoir18, each of which is described below. Each aspect of the apparatus 10may operate independently of the other, or they may be interrelated,e.g., based upon one or more related parameters.

The apparatus 10 may be operated using one or more optional methods,such as those described below, to increase efficiency or otherperformance characteristics of the apparatus 10. For example, based uponmeasurements of pressure and/or oxygen purity, the operating conditionsof the apparatus 10 may be adjusted to increase oxygen purity and/orconcentration, output flow rate and/or pressure, reduce powerconsumption, and the like.

In exemplary embodiments, the apparatus 10 may have the capability todeliver up to about 0.9 or 1.2 liters per minute (lpm) equivalent ofpure oxygen. As used herein, equivalent flow rates may be used, whichcorrespond substantially to the amount of pure (100%) oxygen gasdelivered per unit of time. Because the apparatus 10 concentrates oxygenby adsorption from ambient air, the apparatus 10 does not generate pureoxygen for delivery to a user. Instead, the gas that escapes from thesieve beds 12 that is stored in the reservoir 18 may have a maximumconcentration of oxygen of about ninety five percent (95.4%), with therest of the gas being argon and other trace gases (about 4.6%).

At a given flow rate, the actual amount of concentrated oxygen deliveredby the apparatus 10 may be less than for pure oxygen. Thus, concentratedoxygen may have less therapeutic value than pure oxygen. To compensatefor this deficit and provide equivalent volumes of oxygen, the flow rateof concentrated oxygen must be higher than for pure oxygen. The ratio ofdelivered concentrated oxygen to equivalent pure oxygen is:

Ratio=(100%−21%)/(actual purity−21%), as shown in FIG. 11.

For example, 1.05 lpm of 88% concentrated oxygen may be substantiallyequivalent to 0.9 lpm of pure oxygen and 1.4 lpm of 88% concentratedoxygen may be substantially equivalent to 1.2 lpm of pure oxygen.

Testing has shown that compensating for purity by increasing the flowrate may reduce overall power consumption for the apparatus 10. When thecompeting values of oxygen purity and power consumption are balanced,oxygen purities between about 85-90% may result in desirableefficiencies, with 88% being an exemplary target oxygen purity for thegas delivered by the apparatus 10 to a user.

Generally, to generate concentrated oxygen (which may be stored in thereservoir 18 and/or delivered directly to the user), the apparatus 10 isoperated such that the sieve beds 12 are alternatively “charged” and“purged.” When a sieve bed 12 is being charged or pressurized,compressed ambient air is delivered from the compressor 14 into the airinlet/outlet end 32 of the sieve bed 12, causing the sieve material toadsorb more nitrogen than oxygen as the sieve bed 12 is pressurized.While the nitrogen is substantially adsorbed by the sieve material,oxygen escapes through the oxygen inlet/outlet end 34 of the sieve bed12, where it may be stored in the reservoir 18 and/or be delivered tothe user.

Once the pressure within the sieve bed 12 reaches a predetermined limit(or after a predetermined time), the sieve bed 12 may then be purged orexhausted, i.e., the air inlet/outlet end 32 may be exposed to ambientpressure. This causes the compressed nitrogen within the sieve bed 12 toescape through the air inlet/outlet end 32, e.g., to pass through theair manifold 16 and exit the exhaust opening(s) 92. Optionally, as thesieve bed 12 is being purged, oxygen escaping from the other sieve bed12 (which may be being charged simultaneously) may pass through thepurge orifice 81 into the oxygen inlet/outlet end 34 of the purgingsieve bed 12, e.g., if the pressure within the charging sieve bed isgreater than within the purging sieve bed, which may occur towards theend of purging. In addition or alternatively, oxygen may pass throughthe check valves 10 between the sieve beds, e.g., when the relativepressures of the sieve beds 12 and the reservoir 18 causes the checkvalves 110 to open, in addition to or instead of through the purgeorifice 81. This oxygen delivery into the oxygen inlet/outlet end 34 ofthe sieve bed 12 being purged may assist evacuating the concentratednitrogen out of the sieve bed 12 before it is charged again.

The size of the purge orifice 81 may be selected to allow apredetermined oxygen flow rate between the charging and purging sievebeds 12. It is generally desirable that the flow through the purgeorifice 81 is equal in both directions, such that both sieve beds 12 maybe equally purged, e.g., by providing a purge orifice 81 having ageometry that is substantially symmetrical. In an exemplary embodiment,the purge orifice 81 may have a diameter or other equivalentcross-sectional size of about 0.02 inch (0.5 mm) such that about 2.6 lpmmay pass therethrough at about five pounds per square inch (5 psi)pressure difference across the purge orifice 81. This capacity of thepurge orifice 81 may not correspond to the actual volume of oxygen thatmay flow between the sieve beds 12 during operation of the apparatus 10,since the actual flow may be based the pressure difference between thecharging and purging sieve beds 12, which changes dynamically based uponthe various states of the apparatus 10.

In an exemplary embodiment, shown in Table 2 below, the apparatus 10 maybe operated using a process that includes four (4) states. “1” and “0”represent open and closed states of the air control valves 20,respectively.

TABLE 2 Valve Valve Valve Valve State Time Description 20a_(s) 20a_(e)20b_(s) 20b_(e) 1 Time Pres- Pressurize 12a 1 0 0 1 surize ~6 Exhaust12b sec. 2 Time Over- Pressurize both 12a 1 0 1 0 lap ~0.2 sec and 12b 3Time Pres- Pressurize 12b 0 1 1 0 surize ~6 Exhaust 12a sec. 4 TimeOver- Pressurize both 12a 1 0 1 0 lap ~0.2 sec and 12b

During State 1, sieve bed 12 a is being charged and sieve bed 12 b isbeing purged. As shown in the table, supply air control valve 20 a _(s)and exhaust air control valve 20 b _(e) are open, and supply air controlvalve 20 b _(s) and exhaust air control valve 20 a _(e) are closed. Withadditional reference to FIG. 6, with this valve arrangement, sieve bed12 a communicates with the compressor 14 via compressor outlet passage64 and sieve passage 66 a, while sieve bed 12 b communicates withexhaust opening(s) 92 via sieve bed passage 66 b and exhaust passage 68.At the end of state 1, as the pressure within sieve bed 12 a exceeds thepressure within sieve bed 12 b, the purge orifice 81 provides a low flowof oxygen gas to flush remaining nitrogen from sieve bed 12 b. State 3is the mirror image of State 1, i.e., sieve bed 12 b is being chargedand sieve bed 12 a is being purged.

The duration of States 1 and 3 (Time Pressurize) may be set based uponone or more parameters, such as the size of the purge orifice 81, thepurity of oxygen leaving the sieve beds 12, pressure within thereservoir 18, and the like, as described further elsewhere herein. Forexample, during State 1, if Time Pressurize is too long, all remainingnitrogen in sieve bed 12 b (which is being purged) may be purged, andoxygen from sieve bed 12 a (which is being charged) passing through thepurge orifice 81 into sieve bed 12 b may escape out the exhaustopening(s) 92, wasting oxygen. If Time Pressurize is too short, nitrogenmay remain in sieve bed 12 b at the end of the purge cycle, which mayreduce the efficiency of the sieve bed 12 b when it is subsequentlycharged. Thus, it may be desirable to hold the size of the purge orifice81 to a very tight flow tolerance, and manufacture the sieve beds 12under strict control, such that performance of the sieve beds 12 isconsistent within allowable tolerances without having to adjust TimePressurize during and/or after manufacturing.

During State 2, supply air control valve 20 b _(s) is opened and exhaustair control valve 20 a _(e) is closed. This allows pressurized air fromsieve bed 12 a to flow into sieve bed 12 b through the purge orifice 81.Generally, State 2 is relatively short compared to States 1 and 3, e.g.,such that pressurized air enters sieve bed 12 b before concentratednitrogen within sieve bed 12 a begins to enter sieve bed 12 b. State 2may reduce the amount of compressed air that must be delivered from thecompressor 14 before State 3, which may improve overall efficiency ofthe apparatus 10. Similarly, during State 4, supply air control valve 20a _(g) is opened and exhaust air control valve 20 b _(e) is closed.Thus, during State 4, compressed air flows from sieve bed 12 b to sievebed 12 a before sieve bed 12 a is charged (when State 1 is repeated).

In the embodiment shown in Table 2 above, the durations (Time Overlap)of States 2 and 4 are substantially shorter than the durations (TimePressurize) of States 1 and 3. For example, the durations (Time Overlap)of States 2 and 4 may be not more than about 1.5 seconds or not morethan about 0.6 second, while the durations (Time Pressurize) of States 1and 3 may be at least about four (4) seconds or at least about five (5)seconds.

Optionally, one or more of the durations may be varied, for example, asuser demand (e.g., dose setting and/or breathing rate) and/or otherparameters warrant the change(s). Alternatively, the durations (TimePressurize and Time Overlap) may be fixed when the controller 22 isinitially programmed and/or subsequently serviced. In either case, timesor time constants may be saved in flash-type memory or other memoryassociated with the controller 22. If desired, the times or timeconstants may be adjusted, e.g., via a serial connection during initialmanufacturing, in a subsequent service environment, and/or during use,and the new values may be stored within the memory.

For example, it may be desirable to reduce the durations of States 1 and3 (Time Pressurize) as the pressure within the reservoir 18 (“reservoirpressure” or P_(res)) increases. As the reservoir pressure increases,the higher pressure may drive more gas through the purge orifice 81,reducing the amount of time required to substantially exhaust nitrogenfrom the sieve bed 12 being purged. An equation may be created todetermine the optimum time (Time Pressurize) based upon the reservoirpressure. For example, the equation may be estimated based upon a linearrelationship:

Time Pressurize=k*P _(res).

where k is a constant that may be determined theoretically orempirically. Alternatively, a more complicated equation may bedeveloped, e.g., based upon empirical testing. The duration of States 2and 4 (Time Overlap) may also be fixed or adjusted during manufacturingor servicing, and/or dynamically during operation of the apparatus 10,if desired, in a similar manner.

Optionally, one or more check valves (not shown) may be provided in theexhaust line (e.g., within the exhaust passage 68 in the air manifold 16or coupled to the exhaust opening(s) 92). Such a check valve may stopthe sieve beds 12 from “breathing,” e.g., when the apparatus 10 is notoperational, and is subjected to changing barometric pressure and/ortemperature. For example, if SMC DXT valves are provided for the exhaustair control valves 20 _(e), they may act as check valves. Without pilotpressure, however, the exhaust air control valves 20 _(e) may leak.Relatively small springs (not shown) may be added to these valves toprevent such leakage.

Alternatively, one or more valves (not shown) may be provided inparallel with or instead of the purge orifice 81, i.e., in linesextending between the oxygen inlet/outlet ends 34 of the sieve beds 12.In this alternative, the apparatus 10 may be operated using a four (4)state cycle similar to that described above. However, the parallelvalves may open during the overlap time or at the end of the pressurecycle in order to actively control pressurization or purging of thesieve beds 12.

With concentrated oxygen stored in the reservoir 18 and/or with thesieve beds 12 separating oxygen from ambient air, the apparatus 10 maybe used to deliver concentrated oxygen to a user. As described above,the controller 22 may be coupled to the oxygen delivery valve 116 foropening and closing the oxygen delivery valve 116 to deliver oxygen fromthe reservoir 18 to a user of the apparatus 10.

In an exemplary embodiment, the controller 22 may periodically open theoxygen delivery valve 116 for predetermined “pulses.” During pulsedelivery, a “bolus” of oxygen is delivered to the user, i.e., the oxygendelivery valve 116 is opened for a predetermined pulse duration, andthereafter closed until the next bolus is to be delivered.Alternatively, the controller 22 may open the oxygen delivery valve 116for continuous delivery, e.g., throttling the oxygen delivery valve 116to adjust the flow rate to the user. In a further alternative, thecontroller 22 may periodically open and throttle the oxygen deliveryvalve 116 for a predetermined time to vary the volume of the bolusdelivered.

In one embodiment, the controller 22 may open the oxygen delivery valve116 after the controller 22 detects an event, such as detecting when theuser begins to inhale. When the event is detected, the oxygen deliveryvalve 116 may be opened for the predetermined pulse duration. In thisembodiment, the pulse frequency or spacing (time between successiveopening of the oxygen delivery valve 116) may be governed by andcorrespond to the breathing rate of the user (or other event spacing).The overall flow rate of oxygen being delivered to the user is thenbased upon the pulse duration and pulse frequency.

Optionally, the controller 22 may delay opening the oxygen deliveryvalve 116 for a predetermined time or delay after the user begins toinhale, e.g., to maximize delivery of oxygen to the user. For example,this delay may be used to maximize delivery of oxygen during the“functional” part of inhalation. The functional part of the inhalationis the portion where most of the oxygen inhaled is absorbed into thebloodstream by the lungs, rather than simply used to fill anatomicaldead space, e.g., within the lungs. It has been found that thefunctional part of inhalation may be approximately the first half and/orthe first six hundred milliseconds (600 ms) of each breath. Thus, thepredetermined delay after detecting inhalation may be between abouttwenty and one hundred fifty milliseconds (20-150 ms.).

Thus, it may particularly useful to detect the onset of inhalation earlyand begin delivering oxygen quickly in order to deliver oxygen duringthe functional part of inhalation. A user breathing through their nosemay generate relatively strong pressure drops, e.g., about onecentimeter of water (1 cmH2O), within the cannula. However, if the userbreathes through their mouth, they may only generate pressure drops onthe order of 0.1 centimeter of water (0.1 cmH2O).

For example, assuming an excitation voltage of five volts (5 V), theoutput sensitivity of the pressure sensor 122 may be about 320 μV/cmH2O.Consequently, a pressure drop of 0.1 V (e.g., from inhalation throughthe mouth). If the controller 22 includes an amplifier (not shown)having a gain of one thousand (1,000), the amplifier would create anamplified signal of about thirty two millivolts (322 mV), which mayprovide six (6) counts in a ten (10) bit five volt (5 V) analog todigital (A/D) converter.

As explained above, the pressure sensor 122 may exhibit drift problems,making it difficult for the controller 22 to identify the beginning ofan inhalation and open the oxygen delivery valve 116. One solution is toreset or zero the pressure sensor 122 when the apparatus 10 is off.However, the pressure sensor 122 may be temperature sensitive such thatthe pressure sensor 122 may create a drift greater than the triggerlevel.

Alternatively, as described above, a small valve (not shown) may becoupled to the pressure sensor 122 that may be opened periodically toreset or zero the pressure sensor 122, e.g., while the oxygen deliveryvalve 116 is open and delivering oxygen. In a further alternative, alsodescribed above, a relatively small orifice may be provided between thepressure sensor 122 and the oxygen delivery valve 116 that may allow thepressure sensor 122 to reset or zero during oxygen delivery, e.g.,during a pulse as short as one hundred milliseconds (100 ms.).

In yet a further alternative, the controller 22 may include hardwareand/or software that may filter the signals from the pressure sensor 122to determine when the user begins inhalation. In this alternative, thecontroller 22 may need to be sufficiently sensitive to trigger theoxygen delivery valve 116 properly, e.g., while the user employsdifferent breathing techniques. For example, some users may practicepursed lip breathing, e.g., inhaling through their nose and exhalingthrough pursed lips. During this breathing technique, the controller 22will not detect an expiratory signal that will indicate that inhalationis about to begin.

The filtering algorithm may also need to distinguish between the onsetof inhalation and a declining rate of exhalation, which may otherwisemislead the controller 22 into triggering oxygen delivery during a longperiod of exhalation (which is wasteful). In addition or alternatively,the filtering algorithm of the controller 22 may need to “hold off”during long breaths, e.g., to avoid delivering multiple pulses during arelatively long single inhalation. For example, if the controller 22 isconfigured to open the oxygen delivery valve 16 if it detects a pressuredrop below a predetermined threshold, it may open the oxygen deliveryvalve 116 twice during a single inhalation (which may also be wasteful).In this situation, the filtering algorithm may include a hold-off timeafter inhalation is sensed, e.g., at least about 1.5 seconds.

Alternatively, the controller 22 may open at a pulse frequency that maybe fixed, i.e., independent of the user's breathing rate, or that may bedynamically adjusted. For example, the controller 22 may open the oxygendelivery valve 116 in anticipation of inhalation, e.g., based uponmonitoring the average or instantaneous spacing or frequency of two ormore previous breaths. In a further alternative, the controller 2 mayopen and close the oxygen delivery valve 116 based upon a combination ofthese parameters, e.g., based upon the user's breathing rate, butopening the oxygen delivery valve 116 if a minimum predeterminedfrequency is not met.

For pulse delivery, the pulse duration may be based upon the dosesetting selected by the user. In this way, substantially the same volumeof oxygen may be delivered to the user each time the oxygen deliveryvalve 116 is opened, given a specific dose setting. The dose setting maybe a quantitative or qualitative setting that the user may select. Aqualitative dose setting may involve a dial or one or more buttons(e.g., on the user interface 144) that allow the user to select a level,e.g., on a scale from one to ten (1-10) or from ranging from Minimum toMaximum. The controller 22 may relate the qualitative setting with adesired flow rate or bolus size, e.g., relating to the maximum flowcapacity of the apparatus 10.

For example, the settings may correspond to points within the range atwhich the apparatus 10 may supply concentrated oxygen, e.g., betweenzero and one hundred percent (0-100%) of a maximum capacity of theapparatus 10. For example, a maximum flow rate (or equivalent flow rateof pure oxygen) for the apparatus 10 may be used, e.g., between aboutsix and sixteen liters per minute (6-16 lpm). Alternatively, a maximumbolus volume may be used, e.g., between about ten and one hundred fiftymilliliters (10-150 mL) or between about ten and eighty milliliters(10-80 mL).

A quantitative setting may allow a user to select a desired flow rate(e.g., in lpm), which may be an actual concentrated oxygen flow rate oran equivalent pure oxygen flow rate, or a desired bolus volume (e.g., inmilliliters). The flow rates or volumes available for selection may alsobe limited by the capacity of the apparatus 10, similar to thequalitative settings. Additional information on using a volume-baseddose setting system, rather than implying equivalency to continuousflow, may be found in Characteristics of Demand Oxygen Delivery Systems:Maximum Output and Setting Recommendations, by P. L. Bliss, R. W. McCoy,and A. B. Adams, Respiratory Care 2004; 49(2) 160-165, the entiredisclosure of which is incorporated by reference herein.

As the dose setting is increased, the pulse duration may be increased,e.g., from about fifty to five hundred milliseconds (50-500 ms) todeliver a predetermined bolus during each pulse. If the user's breathingrate remains substantially constant, the pulse frequency may also remainsubstantially constant, thereby increasing the overall flow rate beingdelivered to the user. During actual use, however, the user's breathingrate may change, e.g., based upon level of activity, environmentalconditions, and the like. For example, breathing rates for lung diseasepatients may vary from about thirteen to forty (13-40) breaths perminute, or from about eighteen to thirty (18-30) breaths per minute.Therefore, the apparatus 10 may be capable of delivering thesefrequencies of pulses to the user.

Because of the relatively small size of a portable concentrator, such asapparatus 10, conditions may occur in which the dose setting and user'sbreathing rate exceed the capacity of the apparatus 10. Thus, for anygiven dose setting, i.e., particular volume (e.g., mL) per breath, theapparatus 10 may have a maximum breathing rate at which the apparatus 10may deliver oxygen at the desired dose setting.

If the maximum breathing rate for a particular dose setting is exceeded,the apparatus 10 may respond in one or more ways. For example, theapparatus 10 may include an alarm, e.g., a visual and/or audio alarm,that may alert the user when such an event occurs. This may alert theuser, and, if necessary, the user may slow their breathing rate, e.g.,by resting and the like.

In addition or alternatively, the apparatus 10 may change the deliveryparameters to maintain delivery at or near the maximum flow ratecapacity of the apparatus 10, e.g., about 900 mL/min. or about 1,200mL/min. To achieve this, the controller 22 may calculate the bolus sizethat may be delivered given the user's breathing rate (e.g., dividingthe maximum flow rate by the breathing rate or using a lookup table),and adjust the pulse duration accordingly (and/or throttle the oxygendelivery valve 116). For example, assume the controller 22 detects thatthe user has a breathing rate of about twenty three breaths (23) perminute over a predetermined time, e.g., the most recent thirty seconds(30 s.), and the dose setting delivers forty millimeters (40 mL) perbreath. The resulting flow rate, 920 mL/min. would exceed the ability ofa 900 mL/min. capacity apparatus. Consequently, the controller 22 mayreduce the pulse duration to reduce the flow rate at or below 900mL/min, e.g., by reducing the pulse duration by at least about(1-900/920) or about percent two percent (2%).

When selecting volumetric flow rates for pulse delivery, one or moreadditional factors may also be considered. For example, higher flowrates may create greater back pressure in the cannula, making control ofthe flow more difficult, especially in a relatively low pressure system,such as a portable oxygen concentrator, similar to the apparatus 10described herein.

Optionally, the apparatus 10 may be operated in a manner that maymaximize efficiency, e.g., to reduce power consumption and extendbattery life of the apparatus 10. This may enhance the mobility of theuser, e.g., allowing them to remain independent of an external powersource for longer periods of time.

Several variables may be relevant to determine how much energy may berequired to operate the apparatus 10. The independent variable is thespeed or power of the compressor 14, which may consume as much as ninetyfive percent (95%) of the power used by the apparatus 10. The speed ofthe motor 40 of the compressor 14 may be controlled by the controller22, and is essentially a pulse width modulation (“PWM”) of the power ofthe battery 148, i.e., the more power required, the higher the dutycycle of the PWM.

Closed loop speed or torque control of the motor 40 may be used, but maynot be necessary. During the process cycle, as pressure increases, thespeed of the motor 40 of the compressor 14 may be reduced because of thehigher torque requirement. This may result in the total energy requiredbeing substantially leveled, minimizing current peaks.

The PWM may be expressed as a percentage from zero to one hundred(0-100%), zero corresponding to the compressor 14 being off and onehundred percent corresponding to the compressor 14 operating at itsmaximum speed. In practice, there is a minimum value attainable, belowwhich the compressor 14 may not turn, and therefore, the true range maybe about forty to one hundred percent (40-100%). The equations hereassume the relationships are linear, which may provide sufficientapproximation. Alternatively, more detailed equations may be developedbased upon theoretical or empirical calculations, e.g., which may beimplemented using a non-linear equation or a lookup table, e.g., withinmemory of the controller 22.

PWM may be controlled by monitoring reservoir pressure within thereservoir 18) and controlling the motor 40 of the compressor to maintaina target reservoir pressure. For example, the controller 22 may becoupled to pressure sensor 114 within the reservoir to monitor thereservoir pressure, and the controller 22 may adjust the PWM of themotor 40 accordingly. The target reservoir pressure may be static, e.g.,set during manufacturing or service, or may be dynamic, e.g., changed tomaintain a target oxygen purity and/or other parameter(s), as describedfurther elsewhere herein. Alternatively, multiple variables may bemonitored and the motor 40 controlled to maintain the multiple variablesat selected targets.

For example, a target reservoir pressure may be selected based upon dosesetting and user breathing rate. In exemplary embodiments, the targetreservoir pressure may be between about five and fifteen pounds persquare inch (5-15 psi) or between about six and twelve pounds per squareinch (6-12 psi). Optionally, the target pressure may be adjusted basedupon other parameters, such as oxygen purity, as explained furtherbelow.

The user breathing rate may be determined by the controller 22, e.g.,based upon pressure readings from the pressure sensor 122. The pressuresensor 122 may detect a reduction in pressure as the user inhales (e.g.,drawing oxygen from the recesses 133, 137 and channel 135, shown inFIGS. 8A and 8B). The controller 22 may monitor the frequency at whichthe pressure sensor 122 detects the reduction in pressure to determinethe breathing rate. In addition, the controller 22 may also use thepressure differential detected by the pressure sensor 120.

As the dose setting is increased, the user breathing rate increases,and/or the battery voltage drops, the product reservoir pressure maytend to drop. To compensate for this pressure drop, PWM may beincreased. Thus, a target reservoir pressure may be chosen and thecontroller 22 may implement a control loop to maintain this targetreservoir pressure.

In addition, the oxygen sensor 118 may also be used to monitor thepurity of the oxygen being delivered from the reservoir 18. Changes inthe oxygen purity may be affected by the condition of the sieve materialwithin the sieve beds 12, the temperature and/or the humidity of theambient air being drawn into the apparatus 10 to charge the sieve beds12, and the like. The controller 22 may have a set target oxygen puritystored in memory, e.g., between about 85-93%, such as 88%, and maymonitor the purity detected by the oxygen sensor 118. If the oxygenpurity decreases below the target oxygen purity, the controller 22 mayincrease the target reservoir pressure to compensate and increase theoxygen purity. This may trigger the controller 22 increasing PWM basedupon the control loop used by the controller 22 to maintain the newtarget reservoir pressure.

Thus, the controller 22 may modify PWM, i.e., the speed of the motor 40of the compressor 14, to maintain the reservoir near its targetpressure, which the controller 22 may modify based upon the parametersmonitored by the controller 22.

The maximum oxygen production rate is dependent upon the speed of thecompressor 14, which, in turn, is dependent upon the input voltage fromthe batteries 148. To operate effectively, it is desirable for theapparatus 10 to operate at or close to the target parameters, even asthe batteries 148 begin to deplete their charges. For a 4S4P Li-Ionbattery, the voltage at the end of the battery's charge may be abouteleven Volts (11 V). When this battery is fresh (or when the apparatus10 is connected to an external power source), by comparison, the voltagemay be as much as 16.8 Volts. To prevent excess oxygen generation whenthe batteries 148 are fully charged, it may be desirable to impose amaximum speed for the compressor 14, e.g., not more than about 2,500rpm. Alternatively, the controller 22 may allow this maximum speed to beoccasionally exceeding within a predetermined margin of safety, in orderto reduce the risk of damage to the compressor 14.

By way of example, for an apparatus 10 delivering up to sixtymilliliters (60 mL) per breath, an exemplary flow rate of about eightliters per minute (8 μm, or about 133 mL/s.) may be used. The equivalentvolume of 88% oxygen gas is about seventy milliliters (70 mL), and thepulse duration would be about 0.53 second. If the apparatus 10 iscapable of generating up to about 1200 mL/min, the maximum breathingrate at maximum dose setting would be about seventeen (17) breaths perminute. Assuming an I:E ratio of 1:2 and that the first fifty percent(50%) of each of the user's breaths are functional (and not fillingdead-space), the minimum available time would be 0.60 second. At higherbreathing rates, the maximum pulse volume (and pulse duration) would belower because of the maximum production rate.

Since the apparatus 10 may operate at relatively low pressures, e.g.,between about five and twelve pounds per square inch (5-12 psi), theflow through any controlling passage within the apparatus 10 will not besonic. Consequently, if the back pressure of the apparatus 10 varies,e.g., due to the cannula or tubing connected by the user, it may causechanges in the flow rate of oxygen delivered to the user. At eightliters per minute (8 lpm), the resistance of cannula may be betweenabout 0.7 and two pounds per square inch (0.7-2 psi), e.g., for a Hudsoncannula or a TTO catheter was approximately. This increased backpressure may reduce the flow rate of oxygen delivered to the user by asmuch as twenty five percent (25%).

To allow for variance in both reservoir pressure and downstream pressure(pressure from the reservoir 18 to the user via the cannula), thefollowing algorithm may be employed. The valve “on time” may be adjustedto maintain a fixed pulse volume (as set by the selected dose setting).The reservoir pressure may be measured during the time that the oxygendelivery valve 166 is off, and the pressure across the oxygen deliveryvalve 116 may be measured, e.g., using pressure sensor 120, while theoxygen delivery valve 116 is open.

Valve On Time or the pulse duration (Time Delivery in Table 3) may beset as a factor of dose setting adjusted by oxygen purity to get actualvolume, reservoir pressure, and pressure drop across the oxygen deliveryvalve 116. The equations that may be used for these calculations areshown in Table 3, which includes exemplary control parameters that maybe used to operate the apparatus 10.

TABLE 3 Start Parameter Type Units Range Value Definition TimePressurize Calc. sec 4-12 6 Pressure Product PsiF × Time PressurizeGain + Time Pressurize Offset. This parameter may be calculated fromTarget pressure instead of measured. Shorter time creates lowerpressure. Time Pressurize Set sec/psi 0-(−.6) −0.3 Gain Time PressurizeSet sec 0-20 9 Offset Time Overlap Set sec 0-2  0.2 Reservoir PressureMeas PSI 0-15 8 Measured from Product Trans. from sensor 114 inreservoir with oxygen delivery valve 116 closed. Pressure Product CalcPSI 0-15 8 The controller 22 may include a low pass filter with a timeconstant about thirty seconds (30 s.) to filter out breath and cyclevariations. Pressure Valve Psi Meas PSI 0-15 Measured from ProductTrans. using sensor 114 with oxygen delivery valve 116 open. Themeasurement may be delayed after oxygen delivery valve 116 is opened,e.g., at least about 100 ms to avoid artifact. Pressure Valve Calc PSI0-15 7 The controller 22 may include a low PsiF pass filter, e.g., witha time constant of about 100 ms, to filter out noise. O2 Percent Meas21-96  Measured from oxygen sensor 118. O2 Percent F Calc 21-96  80 Thecontroller may include a low pass filter, e.g., with a time constant ofabout 30 s., to eliminate cycle variations. O2 Percent Target Set 75-92 Control Algorithm Target O2Percent (resolution .01) Pulse Vol mL Set mL10-60  Set by patient, equivalent dose of 100% O2 gas Pulse Vol Act mLCalc mL 11-80  Actual Delivered Volume = 79/ (O2PercentTarget − 21) ×PulseVolmL could use O2Percent instead of Target, but may be lessstable, as volume will go up as % goes down, which in turn could cause %to decrease further Time Resp Sec Meas sec 1-5  Measured time betweenlast two breaths Time Resp Sec F Calc sec 1.5-5   3 Low pass filtered5-10 breaths Production Vol Calc mL/min  0-1500 Pulse Vol mL × 60/TimeResp Sec mL F Pressure Product Calc PSI 3-12 (Pressure Product TargetGain × Target Psi Production Vol mL + Pressure Product Target Offset) ×O2 Factor Pressure Product Set PSI/mL/  0-.03 0.01 Target Gain minPressure Product Set PSI 0-12 3 Target Offset O2 Factor Calc none .5-1.51 O2 Factor(old value) × (O2 Percent Target − O2 Percent F) × O2 FactorGain O2 Factor Gain Set none Depends on how often updated, but shouldchange gradually, over 1-20 minutes Motor Pwm Calc min-100 Motor Pwm(oldvalue) × (Pressure Product Psi F − Pressure Product Target Psi) × MotorPwm Gain. Closed loop control to obtain PressureProductTargetPSI MotorPwm Min Set 0-50 50 Minimum and startup PWM value, to avoid non-rotatingpump Motor Pwm Gain Set Sets how rapid motor control changes are -depends on how often updated - control may change somewhat rapidly,because product pressure is already filtered. Time Delivery Calc Msec100-700  (Pulse Vol Act mL × Pressure Valve Msec Psi F{circumflex over( )}0.5 × Time Delivery Gain)/ ((Pressure Product Psi + 14.2). Time tohold the delivery valve open - needs more empirical validation TimeDelivery Set none 50-200 100 Gain

In an alternative embodiment, a valve (not shown) may be provided thatmay act similar to a pressure regulator. Instead of controlling thedownstream gauge pressure, it may control a pressure drop across anorifice placed inline downstream with the delivery valve. In this way,regardless of downstream pressure, the same flow rate may be delivered,and the resulting volume at a selected pulse duration may besubstantially constant.

When a user decides to turn off or shut down the apparatus 10, e.g., bydepressing an on/off switch or depressing a “button” on a touch screen,e.g., on the user interface 144, it may desirable for the apparatus 10to complete a procedure automatically to protect the apparatus 10. Forexample, if pressurized air remains in the sieve beds 12 after shutdown,water in the air may condense or otherwise be absorbed by the sievematerial, which may damage the sieve material. It may also be desirableto substantially isolate the sieve beds 12 from atmospheric conditions,e.g., to prevent the sieve beds 12 from “breathing” when the apparatus10 encounters changing barometric pressure and/or temperature. Any suchbreathing may introduce air into or evacuate air out of the sieve beds12, which may introduce moisture into the sieve material.

When the apparatus 10 is being turned off, the oxygen delivery valve 116may be closed to discontinue delivery of oxygen from the reservoir 18.The supply air control valves 20 _(s) may be automatically closed(either actively or as the default when electrical power is turned off),e.g., while the exhaust air control valves 20 _(e) are opened. After afirst predetermined time, e.g., between about one hundred and threehundred milliseconds (100-300 ms), the compressor 14 may be turned off.Leaving the compressor 14 operating momentarily after closing the supplyair control valves 20 _(s) may leave residual pressure within the airmanifold 16, which may enhance holding the air control valves 20 _(s)closed for an extended period of time. This pressure may leak slowlyover time.

After a second predetermined time, e.g., between about nine and twelveseconds (9-12 s), allowing any pressurized air to be exhausted from thesieve beds 12, the exhaust air control valves 20 _(e) may be closed(either actively or as the default when electrical power is turned off).

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it is to be understood thatthe present invention contemplates that, to the extent possible, one ormore features of any embodiment can be combined with one or morefeatures of any other embodiment.

1. A portable oxygen concentrator, comprising: a plurality of sieve bedsadapted to absorb nitrogen from air, each sieve bed comprising an airinlet/outlet end and an oxygen inlet/outlet end; at least one reservoircommunicating with the oxygen inlet/outlet ends of the plurality ofsieve beds for storing oxygen exiting from the oxygen inlet/outlet endsof the plurality of sieve beds; a compressor for delivering air at oneor more desired pressures to the air inlet/outlet ends of the pluralityof sieve beds; a set of valves between the compressor and the airinlet/outlet ends of the plurality of sieve beds; a controller coupledto the valves for selectively opening and closing the valves toalternately charge the plurality of sieve beds by delivering compressedair into the plurality of sieve beds through the air inlet/outlet endsto cause oxygen-enriched gas to exit from the oxygen inlet/outlet endsinto the reservoir and purge plurality of the sieve beds by evacuatingpressurized nitrogen from the plurality of sieve beds through the airinlet/outlet ends; and an exhaust passage communicating with the airinlet/outlet ends of the plurality of sieve beds, wherein the exhaustpassage is configured to deliver a flow of nitrogen evacuated from theplurality of sieve beds such that the flow of the nitrogen is directedat or across the controller to cool the controller.
 2. The portableoxygen concentrator of claim 1, further comprising one or more checkvalves between the plurality of sieve beds and the reservoir forpreventing oxygen from flowing from the reservoir into the plurality ofsieve beds.
 3. The portable oxygen concentrator of claim 1, furthercomprising an air manifold providing a plurality of passages thereincommunicating between the compressor and the air inlet/outlet ends ofthe plurality of sieve beds, wherein the valves are coupled to the airmanifold for selectively opening and closing the passages.
 4. Theportable oxygen concentrator of claim 1, the plurality of sieve bedscomprising a first sieve bed and a second sieve bed, the controllerconfigured for periodically opening a first subset of the valves tocharge the first sieve bed and purge the second bed, and opening asecond subset of the valves to charge the second sieve bed and purge thefirst sieve bed.
 5. The portable oxygen concentrator of claim 4, thecontroller further configured for opening a third subset of the valvesto charge the first sieve bed and the second sieve bed between openingthe first subset of the valves and the second subset of the valves. 6.The portable oxygen concentrator of claim 5, the controller configuredfor opening the first subset of the valves and the second subset of thevalves for a first length of time and a second length of time, and foropening the third subset of the valves for a third length of time thatis less than the first and the second lengths of time.
 7. The portableoxygen concentrator of claim 1, further comprising a delivery linecommunicating with the reservoir and a delivery valve communicating withthe delivery line, the controller coupled to the delivery valve forselectively opening and closing the delivery line to deliveroxygen-enriched gas from the reservoir to a user.
 8. The portable oxygenconcentrator of claim 8, further comprising a pressure sensorcommunicating with the delivery line for detecting inhalation by theuser, the controller coupled to the pressure sensor for opening thedelivery valve responsive to inhalation by the user to deliver a pulseof oxygen from the reservoir to the user.
 9. A method for concentratingoxygen comprising: providing a portable apparatus comprising: aplurality of sieve beds, each sieve bed in the plurality of sieve bedsincluding a first end and a second end, a reservoir communicating withthe second ends of the plurality of sieve beds, a compressor, a set ofvalves between the compressor and the first ends of the plurality ofsieve beds, and control electronics adapted to control operation of thevalves; selectively opening and closing the valves to alternately chargethe plurality of sieve beds by delivering compressed air into theplurality of sieve beds through the first ends to cause oxygen-enrichedgas to exit from the second ends into the reservoir and purge theplurality of sieve beds to evacuate pressurized nitrogen from theplurality of sieve beds through the first ends; and directing thenitrogen evacuated from the sieve beds at or across the controlelectronics to cool the control electronics.
 10. The method of claim 9,wherein the step of selectively opening and closing the valves comprisesa cycle including the following sequential steps: a) charging a firstsieve bed while purging a second sieve bed, whereby oxygen-enriched gaspasses from the first sieve bed to the second sieve bed via the purgeorifice; b) simultaneously charging the first and the second sieve bedsto direct gas from the first sieve bed into the second sieve bed; c)charging the second sieve bed while purging the first sieve bed, wherebyoxygen-enriched gas passes from the second sieve bed to the first sievebed via the purge orifice; and d) simultaneously charging the first andthe second sieve beds after step c) to direct gas from the second sievebed into the first sieve bed.